The present invention relates generally to hydrostatically driven vehicles, and more particularly to a neutral start interlock that utilizes non-contacting sensors to monitor the position of the hydrostatic displacement control on such systems used in agricultural and construction.
Agricultural and construction vehicles propelled by engines driving one or more hydraulic pumps, wherein vehicle speed and direction are controlled by the hydraulic pumps are well known. Many such vehicles are propelled by two hydraulic pumps, one for each of a pair of front driving wheels. Direction of travel is controlled by adjusting the relative speeds of the two drive wheels.
Such hydrostatic drive systems are often configured with the hydraulic pump attached directly to the engine without a clutch or other mechanisms to stop rotation of the pump while the engine is running. The vehicle is then subject to movement based on the pump displacement control which most commonly is moved selectively through forward-neutral-reverse positions by the operator.
It is known to provide a neutral start feature on vehicles having hydrostatic drive systems. Neutral start mechanisms are designed to prevent the vehicle engine from being started while the transmission is in a driving, non-neutral mode, and thereby generally prevent the vehicle from lunging forward or turning when started. Conventional neutral start mechanisms tend to add complexity to the overall linkage structure and contribute to a relatively high overall part count for the linkage structure, thus adding to manufacturing and maintenance costs.
Conventional neutral start systems rely on position sensing mechanisms that are typically costly to manufacture and assemble, space consuming, and complex. Conventional position sensing mechanisms typically utilize mechanical connections between transmission control arms and the sensing device which require periodic adjustment and regular maintenance. Such mechanical interconnections may lack the necessary reliability for agricultural applications wherein equipment down time, especially during critical harvest times, jeopardizes the crop and represents a significant economic disadvantage.
It would be a great advantage to provide a neutral start system that replaces the usual mechanical connection mechanism with a non-contacting sensor apparatus to provide a signal to the neutral start system indicating that the vehicle drive pumps are in neutral or indicate the direction the pump controls must be moved to reach neutral thereby overcoming the above problems and disadvantages.